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Title: Structural stainless steel design : resistance based on deformation capacity
Author: Ashraf, Mahmud
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2006
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Since stainless steel is an expensive material, it is important that, when used in structural applications, its particular properties are appropriately taken into account in the design process. At present, design rules tend to treat stainless steel in much the same fashion as carbon steel despite the fundamental differences in the basic material stress-strain behaviour. The cross-section classification approach is well suited for ordinary carbon steel for its idealised elastic, perfectly plastic material behaviour. In the case of stainless steel, material nonlinearity initiates at very low stresses leading to significant strain hardening without showing any yield point. Adoption of the traditional cross-section classification for stainless steel is misleading in terms of material behaviour and also is responsible for the observed conservatism provided by the existing design codes. The primary objective of the present research is therefore to devise a rational continuous design method for structural stainless steel exploiting its special features without doing any cross-section classification. All available test results on material coupons have been analysed to obtain appropriate material models for different grades. Effects of cold-working on the corner regions of stainless steel sections have been investigated and hence proposals have been made for the prediction of the corner strength using the basic material properties. A consistent approach has been adopted to develop numerical models for different cross-sections and members subjected to various types of loading. Measured material and geometric properties, predicted enhanced strength at the cold-worked corners and predicted initial imperfections have been used in highly nonlinear FE models. Once verified against the test results, the FE models have been used to generate useful results where test results are scarce. A continuous relationship between the cross-section slenderness and the deformation capacity has been developed using the available stub column load-deformation results. Corner strength enhancements and post-buckling effects have been appropriately incorporated into the design method to obtain accurate predictions for the compression resistance of cross-sections using the proposed material model. A concept of generalised shape factor, which considers the nonlinear distribution of bending stresses, has been successfully utilised to predict the bending resistance of cross-sections. Once verified for the cross-sections, the basic concept of deformation capacity has been extended to stainless steel members. New sets of column curves have been proposed to predict the flexural buckling resistance. Beam-column interactions have also been investigated and hence recommendations have been made to obtain values for interaction factors to obtain appropriate ultimate load predictions. Comparison between test results and predicted results obtained using the current Eurocode (prEN 1993-1-4, 2004) and the proposed design method has been made. The comparison revealed that the proposed method offers much more accurate and consistent predictions for similar levels of calculation for all the considered cases.
Supervisor: Nethercot, David ; Gardner, Leroy Sponsor: Commonwealth Scholarship Commission ; Bangladesh University of Engineering and Technology
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available